(1) Field of the Invention
The present invention relates to a vibration isolating support apparatus for damping transfer of vibration caused by earthquake or the like at electronic data-processing centers, nuclear reactor equipment, art museums, museums and the other important security institutions.
(2) Related Art Statement
It has been known that the natural frequency of middle and low storied buildings is in a range of about 1.about.2 Hz and the peak frequency of earthquake is in a range of 5.about.10 Hz. Upon earthquake occurrence, however the building resonates with the predominant portion of the seismic wave to increase shaking of the building and consequently substantial damage may occur.
When a computer or the like is set up in such a building, the computer will fall down by the earthquake and be greatly damaged.
In order to prevent such damage, it has been proposed to use a three dimensional vibration isolating support apparatus which is composed of an air spring and a laminated rubber so as to damp both horizontal vibration and vertical vibration simultaneously.
The laminated rubber is constructed by alternately stacking a rubber like elastic material and a reinforcing sheet such as a steel sheet or a hard plastic sheet and then integrally connecting them. It has a stiffness and a high spring constant against a vertical load and a flexibility and a low spring constant against a horizontal load owing to the mechanical properties of the rubber like elastic material. The ratio of vertical and horizontal spring constants is in a range of 100 to 1,000. A support apparatus comprising such a laminated rubber alone has a sufficient vibration isolating function in the horizontal direction, but an insufficient vibration isolating function in the vertical direction.
However, the air spring has an excellent vibration isolating function in the vertical direction.
The aforementioned three dimensional vibration isolating support apparatus is for example, disclosed in Japanese Patent Application Laid-open No. 63-89,751.
The conventional three dimensional vibration isolating support apparatus comprises a large laminated rubber, an inner cylinder secured to one end of the laminated rubber, an outer cylinder surrounding the inner cylinder from an opposite side of the laminated rubber and a diaphragm interposed between the inner cylinder and the outer cylinder to define a closed space which is filled with air under pressure.
Such a conventional three dimensional arrangement has drawbacks as follows.
(i) A large mounting space is required under a floor since a load to be supported by one vibration isolating support apparatus must be large in order to make the shape of the laminated rubber flat and therefore when the vibration isolating support apparatus is used in a vibration isolating floor, the height of the vibration isolating floor becomes higher.
(ii) It is difficult to obtain a sufficient vibration isolating effect since the load must be large in order to make the laminated rubber flat and therefore the natural frequency in the horizontal direction of the vibration isolating support apparatus could not be reduced when the load is small.
(iii) Additional dampers are required in order to restrict a horizontal displacement caused by earthquake when the vibration isolating support apparatus is actually applied to the building.